1. Field of the Invention
The present invention relates to antistatic photosensitive materials and particularly to antistatic photosensitive materials wherein a copolymer containing therein a repeating unit of a maleic acid ester having an ethyleneoxy chain in the main chain is present in a layer of the photosensitive material.
2. Description of the Prior Art
Photosensitive materials are generally composed of a support of a film of a poly-.alpha.-olefin such as polyethylene, or polystyrene, a film of a cellulose ester such as cellulose triacetate, a film of a polyester such as polyethylene terephthalate, a paper, a synthetic paper or a coated paper, and photosensitive emulsion layers and, if desired, intermediate layers, a protective layer, a back layer, an antihalation layer and an antistatic layer, which are provided on one or both surfaces of the support through a subbing layer. Examples of photosensitive materials wherein photographic emulsion layers are applied to both surfaces of the support, are, for example, direct printing X-ray films. However, in most photographic sensitive materials, the photographic emulsion layers are provided on only one surface of the support. Thus, in the latter case, a photographic emulsion is not applied to one surface of the support. Hereinafter such a surface will be designated the back face of the photographic sensitive material. Since photographic sensitive materials comprise a support which is electrically insulating and photographic layers, electrostatic charges often accumulate when the photographic sensitive material rubs in contact with a surface of the same or of different materials or is separated during their production or during their use. The accumulated electrostatic charges cause many difficulties. For example, in a photographic film before developing, the photosensitive emulsion layer is exposed due to a discharge of the accumulated electrostatic charges and, consequently, dot-like spots or branched or feather-like line marks appear on development of the photographic film. These spots are the so-called static marks, which result in a marked deterioration in the commercial value of the photographic film. For example, it can be easily understood that a serious danger can occur when they appear on medical or industrial X-ray films. Since this phenomenon becomes clear for the first time only after development, it is one of the most troublesome problems. Further, the accumulated electrostatic charges cause dust to adhere to the film surfaces and induce secondary difficulties such as uneven coated layers.
These electrostatic charges often accumulate in the production of the photographic sensitive material and on use thereof as described above. For example, they are generated by friction between the photographic film and rolls in production or by separation of the support surface and the emulsion layer surface on winding or rewinding the photographic film. Further, in finished goods, they are generated by separation of the support surface and the emulsion layer surface on rewinding at high humidity so that adhesion of the photographic film occurs, by friction between the film and the metal parts of a camera or a separation of the support surface and the emulsion layer surface during photographing and rewinding of a movie film, or by contact and separation between the film and the mechanical parts of an X-ray automatic photographing machine or a fluorescent sensitizing paper. In addition, they are generated by contact with packing materials. Generation of static marks on photosensitive materials induced by accumulation of electrostatic charges are further increased when the sensitivity of the photographic sensitive materials is increased or when processing rate of the photographic sensitive materials is increased.
Although it is believed that charging by friction or by separation results from an ionic interaction between the molecules present in the contacting materials, it is now difficult to chemically estimate what kind of material can be used to form positive charges and what kind of material can be used to form negative charges. However, it is easily considered that thus electrostatic charging can be prevented by reducing the applied electric voltage or by increasing the electric conductivity of the surface of the materials so that electrostatic charges are dispersed within a very short time before partial discharging occurs due to an accumulation of charges. Accordingly, methods of improving the conductivity of the surface of the support or a coating layer of the photosensitive materials have hitherto been found, and thus use of many kinds of hygroscopic materials, water soluble inorganic salts, surface active agents and polymer has been attempted. For example, the polymers as described in U.S. Pat. Nos. 2,882,157, 2,972,535, 3,062,785, 3,262,807, 3,514,291 and 3,615,531, the surface active agents as described in U.S. Pat. Nos. 2,982,651, 3,428,456, 3,457,076, 3,454,625, 3,552,972 and 3,655,387 and zinc oxide, semiconductors and colloidal silica as described in U.S. Pat. Nos. 3,062,700, 3,245,833 and 3,525,621 are known.
As a method of directly providing the photographic film support with antistatic properties, a process is known which comprises adding such material directly into a high molecular weight material for the support or applying such material to a surface of the support. In the latter case, the antistatic agent can be applied individually or in a combination with a high molecular weight material such as gelatin, polyvinyl alcohol or cellulose acetate to form a backing layer. Further, as a method of providing photographic sensitive material with antistatic properties, a process which comprises incorporating an antistatic agent in a photographic emulsion layer or a surface protective layer thereof or applying a solution of the antistatic agent to the surfaces of these layers is known. However, the above described materials exhibit specific properties depending on the kind of film support or photographic composition. For example, although a certain material may provide a good result with a specific film support and a specific photographic emulsion or another photographic element, it is sometimes not only useless as an antistatic agent for other film supports and other photographic elements but may also adversely influence the photographic properties.
In general, there are few materials which exhibit sufficient effects at low humidity (about 30 percent RH or lower) for high speed emulsions, and sometimes a deterioration of the antistatic effect with the lapse time occurs with such materials and adhesion difficulties at high temperature and high humidity result. Particularly, it is difficult to establish a technique for effectively utilizing the antistatic agents in photosensitive materials wherein a photographic emulsion is applied to both surfaces of the support such as a direct printing X-ray film. Further, although it is desired to obtain photosensitive materials which have a low surface resistivity at a low humidity (about 30 percent RH or less), many difficulties occur in the production of such photosensitive materials. Particularly, a technique of providing such a characteristic to the photographic emulsion layer side has not be found in the prior literature or patents. Furthermore, in finding an antistatic agent for photographic sensitive materials, attention must be paid to not only photographic properties such as sensitivity, fog, granularity or sharpness but also properties such as an appropriate coefficient of friction so that camera behavior is not deteriorated or such as tackiness must be considered. When a certain kind of synthetic surface active agent used for a coating assistant is used as an antistatic agent, the antistatic effect thereof sometimes is markedly reduced. Therefore, a large number of different antistatic agents have been tried since predictions of whether an antistatic agent will be effective in a photographic sensitive material is very difficult.